More particularly, amongst such devices, the invention relates to those comprising:
two rigid frame members suitable for securing to respective ones of the two rigid elements to be united; PA1 an elastomer body interconnecting the two frame members and co-operating therewith to form, at least in part, two sealed chambers; PA1 a constricted passage keeping the two chambers permanently in communication with each other; PA1 a mass of liquid filling the two chambers and the constricted passage; PA1 a valve member in the form of a plate of elastically deformable material defining in part at least one of the two chambers and another chamber which is preferably the second of said two chambers, said valve member having an axis of revolution or the like; and PA1 at least one rid limiting the displacements of said valve member. PA1 the non-uniform means are constituted at least in part by non-repetitive angular non-uniformity in at least one of the surfaces of the grid and of the valve member that come into mutual contact during displacements of said valve member; PA1 the surface non-uniformity is due to its general outline; PA1 the surface non-uniformity is due to the presence of at least one piece of relief projecting relative to its general outline; PA1 one such piece of relief extends over an angle that is no greater than one-fifth of the angle between the outline of the relief and the outline of the closest adjacent relief; PA1 at least one of the pieces of relief is a rib; PA1 at least one of the pieces of relief is a stud; PA1 the non-uniform surface is a contact surface of the grid; PA1 when the valve member is mounted with the possibility of limited deformation between two grids, the surface non-uniformity relates to one only of the two valve member and grid interfaces; PA1 the non-uniform means are constituted, at least in part, by non-repetitive angular non-uniformity in the stiffness of the valve member; PA1 the stiffness non-uniformity of the valve member is due to variations in its thickness; PA1 the stiffness non-uniformity of the valve member is due to at least one insert of different stiffness being incorporated therein; and PA1 at least some of the non-uniform means are disposed close to at least one of the orifices through which the constricted passage opens out into the chambers.
As is known, in such a device, vibration at high frequency and low amplitude, such as the vibration generated by the engine while it is idling, gives rise to a rapid succession of reciprocating deformations of the valve member perpendicularly to itself and suitable for attenuating transmission of the vibration in question.
In contrast, when oscillations are greater in amplitude and lower in frequency, such as the oscillations due to round irregularities and to changes in slope while the vehicle is travelling on the ground the deformations of the valve member reach a maximum possible amplitude and the liquid is transferred from one of the two chambers to the other and back again through the constricted passage, with the mass of liquid driven in this way being caused to resonate when the frequency of the oscillations reaches a predetermined value that is a function of the ratio between the axial length and the right cross-section of the constricted passage. Such resonance serves to provide the desired damping of the oscillations concerned.
The discontinuities in the reciprocating displacements of the valve member, and in particular those due to limits put on valve member displacement by the grid which is associated therewith, give rise to banging and unwanted noise that can be objectionable. This applies in particular to devices fitted to up-market vehicles where it is desired to make their passenger compartments as silent as possible.
A main object of the invention is to mitigate that drawback.
In its French patent application filed under the number 91 03579, the Applicant has already proposed an anti-vibration device of the above-specified type, in which the faces of the valve member include bulges that are integral therewith. During operation of the valve member, the bulges are progressively compressed against the grids that limit displacement of the valve member, after which they expand elastically. More precisely, because of the presence of said bulges, the valve member does not press in an angularly uniform manner against the grids, but is subjected to circumferential undulating deformation: the sections of the valve member on either side of the bulges do not press against the bearing surfaces of the grids as a uniform block, but make angularly progressive contact therewith.
In the embodiments described in the patent application, the outline of the valve member is circular and the bulges are disposed in annular rings, around which they are uniformly distributed.
Anti-vibration devices are also known in which the surfaces of the valve members have multiple projecting irregularities. Those irregularities are distributed over said surfaces in angularly uniform manner, and the presence thereof may lead to a certain amount of attenuation in the above-mentioned banging and unwanted noise.
Even greater attenuation of said banging and unwanted noise can be obtained using the anti-vibration devices proposed by this invention.